The Viral Pathogenesis Core serves as a centralized source for isolates and assays related to HIV-1, HIV-2, and SIV. In addition, the Core acts as an interface between users and the laboratories of UCSD CFAR members specializing in the herpes virus affecting HIV-infected individuals (CMV, HSV, and HHV-8). Four basic types of services are provided: (1) As a viral resource, the Core provides aliquots from a wide collection of characterized and titered viral strains of HIV-1, HIV-2, and SIV. (2) As a cell resource, the Core provides virus susceptible cells, including cell lines, isolated CD4+ T cells and macrophages. (3) As a virus characterization resource, the Core provides testing for cell tropisms, syncytium-inducing (SI) versus non-SI, co-receptor usage, cytopathic versus non-cytopathic, replication kinetics, drug susceptibilities, and other properties of HIV. (4) As a screening service, the Core provides the initial testing for investigational therapeutics (antiviral compounds, gene therapies, antibody neutralization, etc.). These resources make it easier for both novices and experienced investigators to pursue their virological research ideas. Without the Core, each investigator would need to set up and validate the different methods and assays required for their work, which could take months. Also, many of the Core's users have no BL3 training or experience themselves, and thus would need to expend months of effort on gaining the permission needed to work with these viruses. While the Core is not meant to replace a full scale research program set up by an investigator as one of the major projects, it is ideal for conducting pilot experiments and the screening of compounds for antiviral activity.